The clinical role of many drugs currently used to fight opportunistic infections (OIs) and the impact of many potent drugs for OIs coming out of massive drug discovery programs have been hampered by poor watersolubility, high toxicity, and inadequate parenteral dosage forms despite encouraging results in preclinical and clinical testing. Current efforts to address these major bottlenecks in drug development fall in the realm of nanotechnology. In particular, polymeric micelles, nanoscopic supramolecular core-shell structures, have recently entered clinical trials for potent yet poorly water-soluble and toxic drugs, owing to safety, high drug loading, and improved pharmacokinetics. A unique aspect of polymeric micelles is the ability to adjust their chemical structures to fine-tune properties for drug delivery. Our results suggest that adjustments must be made with an individual drug or class of drugs in mind, and that easily made adjustments on poly(ethylene oxide)-block-poly(L-amino acid) (PEG-b-PLAA) micelles may enhance drug delivery. Our efforts focus on amphotericin B (AmB), the primary drug for opportunistic systemic fungal infections. These OIs are a major cause of morbidity among immunocompromised patients suffering from cancer or AIDS and organ transplant recipients. We believe that tailor-made PEG-b-PLAA micelles may increase the therapeutic index of AmB. Specifically, we hypothesize that beneficial changes in the pharmacokinetics of AmB, increased plasma halflife and reduced liver clearance, and changes in its self-aggregation state, owing to PEG-b-PLAA micelles may lower the drug's toxicity and increase its antifungal efficacy. In this context, we may adjust the structure of PEG-b-PLAA micelles to fine-tune the release kinetics of AmB and enhance its delivery. Specific Aims: (1) To study the pharmacokinetics (plasma profile, distribution in plasma, and tissue distribution) of AmB encapsulated by PEG-b-PLAA micelles in rodents. (2) To study the acute, renal and liver toxicity of AmB encapsulated in PEG-b-PLAA micelles in rodents. (3) To study the antifungal activity of AmB encapsulated in PEG-b-PLAA micelles in a neutropenic murine model of disseminated candidiasis. Comparisons will be made with a standard formulation of AmB and a liposomal AmB approved for refractory systemic fungal diseases. These proposed studies will provide insight into mechanisms behind the toxicity and antifungal activity of AmB and perhaps show that PEG-b-PLAA micelles increase the therapeutic index for the drug.